Deployment of photovoltaic (PV) systems in residential settings promises a multitude of environmental and economic advantages, including a sustainable capacity expansion of distribution systems. However, a unique set of challenges related to power quality, efficiency, and reliability may emerge, especially when an increased number of PV systems are deployed in existing distribution networks, and operate according to current practices. One challenge is associated with overvoltages when PV generation exceeds demand. To ensure reliable operation of existing distribution feeders even during peak PV generation hours, recent efforts have focused on the possibility of inverters providing ancillary services.
Secondary-level control of PV inverters can alleviate extenuating circumstances such as overvoltages during periods when PV generation exceeds the household demand, and voltage transients during rapidly varying atmospheric conditions. Initiatives to upgrade inverter controls and develop business models for ancillary services are currently underway in order to facilitate large-scale integration of renewables while ensuring reliable operation of existing distribution feeders
Examples of ancillary services include reactive power compensation, which has been recognized as a viable option to effect voltage regulation at the medium-voltage distribution level. The amount of reactive power injected or absorbed by inverters can be computed based on either local droop-type proportional laws, or optimal power flow (OPF) strategies. Either way, voltage regulation with these approaches comes at the expense of low power factors at the substation and high network currents, with the latter leading to high power losses in the network.